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Tiny
2004-Feb-24, 03:15 AM
What will happen when there is no gravitaional pull in our solar system?
:ph34r: This is not homework question :ph34r: LOL

devilmech
2004-Feb-24, 04:12 AM
Well, as long as there are objects of mass in our solar system, there will always be a gravitational pull. So, I'm not sure what you're asking here.

If, for some reason, gravity decided to take a vacation for a while, then a lot would happen. Planets, asteroids, comets, and other objects in motion orbiting the sun would fly off into space because there is no force keeping them in the solar system. Basically, the solar system would cease to exist

Tiny
2004-Feb-24, 04:21 AM
To tell you the truth, I was doing a research project about Gravitational Force in our solar system, so as a beginner, I only know that the GF keep the objects in our solar system that oribit the sun... So I need someone's opinion or advice about what will happen when there is no GF in our system?

devilmech
2004-Feb-24, 07:42 AM
Originally posted by Tiny@Feb 24 2004, 04:21 AM
I need someone's opinion or advice about what will happen when there is no GF in our system?
I already answered that one:


Planets, asteroids, comets, and other objects in motion orbiting the sun would fly off into space because there is no force keeping them in the solar system. Basically, the solar system would cease to exist

Faulkner
2004-Feb-24, 08:10 AM
If the Sun suddenly, mysteriously "disappeared", everything in orbit around it would begin to fling off in straight line trajectories one by one, starting with Mercury, Venus, Earth (8 minutes later), etc etc... I think it's been confirmed by now that gravity "travels" at the speed of light.

Josh
2004-Feb-24, 08:55 AM
Gravity travels at the speed of light? Okay. I had no idea about that. In fact I don't even think it had occured to me. When I did think about it I found that it's a pretty impressive question!! So I went a'searchin'. Only last year (2003) were there data published to answer this question based on experimental results.

It seems that the debate had been raging whether gravity was instantaneous, travelled at the speed of light, or some greater finite value. Kopeikin and Fomalont were the two to answer this question. Two online articles on their works can be found at New Scientist (http://www.newscientist.com/news/news.jsp?id=ns99993232) and Nature (http://www.nature.com/nsu/030106/030106-8.html).

So the answer? Well according to them it does travel at the speed of light (so as said earlier in the thread Earth would feel no gravity 8 minutes after the suns gravity stopped). The odd thing is though that their error is about 25%. Seems a bit high to say anything with any sort of certainty. If I had an error like that in the experiments I do I'd be told to toss them. The only way to measure the speed of gravity (currently) is using the method Kopeikin and Fomalont used. This only happens once every ten years. Seems like a good reason to not want to toss your results. Essentially then it is possible for gravity to travel faster than the speed of light. 25% faster in fact, which is a whole lot! So why then doesn't the "gravity taking short cuts through other dimensions" theory still hold possibly? It seems to have been dismissed even though faster than light travel of gravity is possible.

NB. I found sites that disagreed with these results but they weren't peer reviewed so I felt it best not to bring them up.

Tiny
2004-Feb-24, 06:44 PM
I think I agree with Josh, no matter how far the planet travel, it can't be fast than the speed of light, unless they is no mass at all... Well thanks for helping me...

devilmech
2004-Feb-24, 08:32 PM
Originally posted by Tiny@Feb 24 2004, 06:44 PM
I think I agree with Josh, no matter how far the planet travel, it can't be fast than the speed of light, unless they is no mass at all... Well thanks for helping me...
umm.... he was making a statement for gravity travelling faster than c, not planets. How did you get planets out of that?

Guest
2004-Feb-24, 08:53 PM
If the Sun's gravity suddenly disappeared, we wouldn't be alive long enough to even worry about it, or even know about it.
on this planet.

Prime

devilmech
2004-Feb-24, 09:18 PM
Originally posted by Guest@Feb 24 2004, 08:53 PM
If the Sun's gravity suddenly disappeared, we wouldn't be alive long enough to even worry about it, or even know about it.
on this planet.

Prime
How so? I imagine there would be quite a few astronomers who would have just enough time to panic as they observed mercury and venus flying off into the distance.

It would also take several hours for the earth cool off enough to become uninhabitable, so we would all survive long enough to say our last goodbyes.

jamerz3294
2004-Feb-24, 09:28 PM
I had never even considered gravity as being able to travel! What a concept to tinker with. But id gravity could travel 25% faster than the speed of light, would that help acount for some the dark energy/matter in the universe?

Guest_bob
2004-Feb-24, 09:37 PM
Originally posted by devilmech+Feb 24 2004, 08:32 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (devilmech @ Feb 24 2004, 08:32 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Tiny@Feb 24 2004, 06:44 PM
I think I agree with Josh, no matter how far the planet travel, it can&#39;t be fast than the speed of light, unless they is no mass at all... Well thanks for helping me...
umm.... he was making a statement for gravity travelling faster than c, not planets. How did you get planets out of that? [/b][/quote]
this is nothing to do with thr subject but we wouldnt of been alive because jupiter nearly became a star&#33; and once a big astriod struck earth and learly destroed it but it never this formed our moon :)

Guest_bob
2004-Feb-24, 09:42 PM
Originally posted by jamerz3294@Feb 24 2004, 09:28 PM
I had never even considered gravity as being able to travel&#33; What a concept to tinker with. But id gravity could travel 25% faster than the speed of light, would that help acount for some the dark energy/matter in the universe?
i agree with jamerz gravity doesnt travel....or maybe it does e.g the moon has gravty and every year it moves like a centimetre :angry:

big steve
2004-Feb-25, 10:09 AM
I have always been told that if there was no gravity then all things on this planet would fly off into space. If the sun were to "lose gravity"then all the planets would fly off into space,or would they be affected by the gravity of the larger planets and be drawn into them?????just a thought

devilmech
2004-Feb-25, 10:28 AM
Originally posted by big steve@Feb 25 2004, 10:09 AM
I have always been told that if there was no gravity then all things on this planet would fly off into space. If the sun were to "lose gravity"then all the planets would fly off into space,or would they be affected by the gravity of the larger planets and be drawn into them?????just a thought
They would all fly off in a straight line trajectory from the point at which the sun&#39;s gravitational pull ceased to affect them. While it is conceivable that the trajectory of some of the planets may be affected by Jupiter, I don&#39;t believe that there&#39;s any reason to believe that they will be drawn into it. Jupiter is over 1000 times less massive than the sun, and therefore exerts a much slighter gravitational pull

damienpaul
2004-Feb-25, 10:44 AM
Not to mention that Jupiter is over 4 times the distance from earth as the sun

Sp1ke
2004-Feb-27, 08:04 AM
would they be affected by the gravity of the larger planets and be drawn into them

If all gravity was switched off, there&#39;d be no gravity to draw the planets together so they&#39;d all continue moving independently in straight lines forever.

But going back to an earlier point, if the gravity disappeared we wouldn&#39;t last long as we wouldn&#39;t be held down on the surface any more. I presume we&#39;d all drift off into space, along with the atmosphere. The people who&#39;d survive longest would be in caves or mines. They should get a few hours extra.

Guest_Faulkner
2004-Feb-27, 08:12 AM
Whoops forgot to log in&#33;

Sp1ke, the issue was if the SUN&#39;s gravity switched off suddenly, not if gravity itself vanished&#33; ;)

Sp1ke
2004-Feb-27, 03:07 PM
Actually, I think both questions have come up in this dialogue - the first post was
What will happen when there is no gravitaional pull in our solar system?

Either way, I think all the planets will fly off in straight lines, their individual gravitational effects on each other being negligible.

As a side question: if the sun was split into loads of little earth-sized chunks that all moved outwards, how far would they have to move before there was an effect on Earth&#39;s orbit? Would the gravitational effects be similar while the chunks were all still inside our orbit? Or would the gravity actually increase as the chunks moved outwards since they&#39;d be closer to us?

QJones
2004-Feb-27, 11:57 PM
I was told (but I can&#39;t remember by who ... so this is TOTALLY not backed up) that if the Earth was hollow, but the same mass, we&#39;d still feel the same gravitational pull toward the centre of the planet (until we got there). So, IF this is correct, then the same would be true of the sun.

Speed of gravity. Actually, measuring the speed of gravity vs. light is not tough, experimentally - it&#39;s just not possible for us:

If you had a 2 balls in space, then they&#39;d affect each other with their gravitational field. You can&#39;t make either ball cease to exist, so you can&#39;t measure speed in that way. However, you can measure the attraction between the balls (using a newton scale). If you moved one ball, you could measure how long it took the other ball to &#39;feel&#39; the movement. (for example, if you moved one ball away, you could measure the time it took before the other ball got &#39;lighter&#39; relative to the first ball).

&#39;course, we can&#39;t do that. But it&#39;s a pretty simple experiment.

For a long time, we didn&#39;t know what would happen - and the constant hope of FTL communication was there (you&#39;d use the two balls as a type of telegraph, if the effect of gravity was instant). Sadly, now, it seems that gravity&#39;s force travels a c. Not a surprise, really.

devilmech
2004-Feb-28, 05:23 AM
Originally posted by QJones@Feb 27 2004, 11:57 PM
I was told (but I can&#39;t remember by who ... so this is TOTALLY not backed up) that if the Earth was hollow, but the same mass, we&#39;d still feel the same gravitational pull toward the centre of the planet (until we got there). So, IF this is correct, then the same would be true of the sun.
Correct with qualifiers. If the earth were hollow, and it&#39;s mass were evenly distributed throughout it&#39;s volume, then it&#39;s barycentric center would lie at the center of the earth. However, the earth isn&#39;t hollow, and no one&#39;s postulated a workable theory of the sun being hollow.

Planetwatcher
2004-Feb-29, 05:50 AM
Originally posted by devilmech+Feb 24 2004, 09:18 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (devilmech @ Feb 24 2004, 09:18 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Guest@Feb 24 2004, 08:53 PM
If the Sun&#39;s gravity suddenly disappeared, we wouldn&#39;t be alive long enough to even worry about it, or even know about it.
on this planet.

Prime
How so? I imagine there would be quite a few astronomers who would have just enough time to panic as they observed mercury and venus flying off into the distance.

It would also take several hours for the earth cool off enough to become uninhabitable, so we would all survive long enough to say our last goodbyes. [/b][/quote]
Don&#39;t count on it. With no gravity there is nothing to keep the air that we breath here on Earth. :huh:
It is likely that our atmosphere would begin to escape and proabley thin out to less then that of Mars in just a few seconds. We would begin to suffacate a few seconds after that. :blink:
If we didn&#39;t first literally explode from our own blood and internal air presures suddenly becoming many hundreds of times greater then our immedate environment. :(
It would be like being a deep sea diver at the bottom of the sea, and having a Star Trek transporter materialize you on the surface without depresuring you. You would become a human bomb. :ph34r:

Since the ability of speech depends on our ability to move air past our vocal cords, we will even lack the ability to speak our goodbyes. :(

As for the planet cooling, the ambient temperture will drop just as fast as we lose air, our best insolater of heat. But at the same time the ground on the sun side will heat up over 300 degrees in that same few seconds. Our planet will be much like that asteroid in movie Deep Inpact when the sun rose on the comet. :ph34r: :ph34r:

So take your pick. A hot foot, hypothermia, having that supernova experience, and/or silent suffacation, and/or all at the same time. :o :angry: :( :ph34r: :blink: :unsure: :huh:

I think I&#39;d rather be at ground zero of a nuclear explosion. :lol:

damienpaul
2004-Feb-29, 06:52 AM
That actually sounds spot on, except for one thing I don&#39;t quite understand...would the internal rotation stay switched on in the earth for a while? due to inertia?

In any case - I&#39;ll join you at ground zero of the nuke, Planetwatcher

Tom2Mars
2004-Mar-02, 09:02 AM
You know, I really can&#39;t believe this&#33; I had been wondering about this for quite awhile and just posted a new question on this, and then started reading the previously posted questions and ran across this thread. Simultaneous, not simutaneous? Is it up in the air then?

devilmech
2004-Mar-02, 09:59 AM
Originally posted by Planetwatcher+Feb 29 2004, 05:50 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Planetwatcher &#064; Feb 29 2004, 05:50 AM)</td></tr><tr><td id='QUOTE'>
Originally posted by devilmech@Feb 24 2004, 09:18 PM
<!--QuoteBegin-Guest@Feb 24 2004, 08:53 PM
If the Sun&#39;s gravity suddenly disappeared, we wouldn&#39;t be alive long enough to even worry about it, or even know about it.
on this planet.

Prime
How so? I imagine there would be quite a few astronomers who would have just enough time to panic as they observed mercury and venus flying off into the distance.

It would also take several hours for the earth cool off enough to become uninhabitable, so we would all survive long enough to say our last goodbyes.
Don&#39;t count on it. With no gravity there is nothing to keep the air that we breath here on Earth. :huh:
It is likely that our atmosphere would begin to escape and proabley thin out to less then that of Mars in just a few seconds. We would begin to suffacate a few seconds after that. :blink:
[/b][/quote]
You seem to forget that gravity travels at &#39;c&#39;. It would take around 8 minutes for us to feel the effect.

Guest
2004-Mar-02, 12:20 PM
It could be that if gravity would cease to exist than you should feel it right away because the warping of space disappears and that results in an infinite speed of the still questionable &#39;maximum&#39; speed for gravitons.
Because &#39;gravitons&#39; are continously emited, they wouldn&#39;t be qeued anymore so the motion of gravitons would directly stop. We wouldn&#39;t have time to react... also if gravity speeds with c, no one should see Mercury flying out of its orbit before gravity stops to exist beforehand. The question is if g goes with speed c or with infinite speed...

degeneration
2004-Mar-03, 12:05 PM
Originally posted by Planetwatcher+Feb 29 2004, 05:50 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Planetwatcher &#064; Feb 29 2004, 05:50 AM)</td></tr><tr><td id='QUOTE'>
Originally posted by devilmech@Feb 24 2004, 09:18 PM
<!--QuoteBegin-Guest@Feb 24 2004, 08:53 PM
If the Sun&#39;s gravity suddenly disappeared, we wouldn&#39;t be alive long enough to even worry about it, or even know about it.
on this planet.

Prime
How so? I imagine there would be quite a few astronomers who would have just enough time to panic as they observed mercury and venus flying off into the distance.

It would also take several hours for the earth cool off enough to become uninhabitable, so we would all survive long enough to say our last goodbyes.
Don&#39;t count on it. With no gravity there is nothing to keep the air that we breath here on Earth. :huh:
It is likely that our atmosphere would begin to escape and proabley thin out to less then that of Mars in just a few seconds. We would begin to suffacate a few seconds after that. :blink:
If we didn&#39;t first literally explode from our own blood and internal air presures suddenly becoming many hundreds of times greater then our immedate environment. :(
It would be like being a deep sea diver at the bottom of the sea, and having a Star Trek transporter materialize you on the surface without depresuring you. You would become a human bomb. :ph34r:

Since the ability of speech depends on our ability to move air past our vocal cords, we will even lack the ability to speak our goodbyes. :(

As for the planet cooling, the ambient temperture will drop just as fast as we lose air, our best insolater of heat. But at the same time the ground on the sun side will heat up over 300 degrees in that same few seconds. Our planet will be much like that asteroid in movie Deep Inpact when the sun rose on the comet. :ph34r: :ph34r:

So take your pick. A hot foot, hypothermia, having that supernova experience, and/or silent suffacation, and/or all at the same time. :o :angry: :( :ph34r: :blink: :unsure: :huh:

I think I&#39;d rather be at ground zero of a nuclear explosion. :lol: [/b][/quote]
Surely that wouldn&#39;t happen if the SUN&#39;s gravity disappeared? Earth would still have gravity, so the atmosphere would still be confined to the Earth.

As long as the heat from the sun was still there, why wouldn&#39;t life on earth continue as normal, for a time at least given that Earth would now be moving in a straight line and getting further from the sun.

a1call
2007-Jul-14, 03:48 AM
Bump. :)
Any new insights as to the speed at which gravity influences matter?

Wouldn't precise observation of the tide offer a clue?

I don't understand why the effect of variation in gravity can't be easily examined .

Tim Thompson
2007-Jul-14, 04:49 AM
General relativity requires that gravity travel at the speed of light. Astronomical observations tend to confirm this expectation. The 1993 Nobel Prize in Physics (http://nobelprize.org/nobel_prizes/physics/laureates/1993/index.html) was awarded to Russell Hulse & Joseph Taylor, for their joint discovery of binary pulsar PSR 1913+16 (http://astrosun2.astro.cornell.edu/academics/courses//astro201/psr1913.htm). The pulsar period is observed to decay at a rate predicted by general relativity, where orbital energy is expected to be converted into gravitational waves, and the waves are generated because of the finite speed of propagation of gravity. The fact that observations match general relativistic expectations is consistent with the general relativistic requirement that the finite speed of gravity is in fact the speed of light. The fact that it travels so fast is the reason that it is not "simple" to see the speed of propagation of gravity. See, i.e., Hulse & Taylor, 1975 (http://adsabs.harvard.edu/abs/1975ApJ...195L..51H); Taylor, et al., 1976 (http://adsabs.harvard.edu/abs/1976ApJ...206L..53T); Taylor, Fowler & McCulloch, 1979 (http://adsabs.harvard.edu/abs/1979Natur.277..437T); Taylor & Weisberg, 1982 (http://adsabs.harvard.edu/abs/1982ApJ...253..908T).

Fomalont & Kopeikin, 2003 (http://adsabs.harvard.edu/abs/2003ApJ...598..704F) claims to have measured the speed of gravity by using a quasar close approach to Jupiter. But their claims are in dispute and have been steadily discussed since then.

a1call
2007-Jul-14, 05:40 AM
Thank you Tim Thompson. The important thing is that we have proof that the speed is finite. Still, with all the technology we have in 21st century (and my simple mind) I expected to have a simple measurement establishing the exact speed.
Of course many questions arise.
* Is the speed reduced through matter as is the case with light?
* Are there phenomena such as refraction, reflection, scattering involved?

EDG
2007-Jul-14, 05:52 AM
But... isn't there a keystone definition in relativity that states that nothing can travel faster than light? I thought that was pretty much an axiom of the whole relativistic approach isn't it? So if that's the case then of course gravity can't travel faster than light, because then it'd be travelling faster than something (i.e. light) that by definition is the fastest that anything can travel?

a1call
2007-Jul-14, 06:16 PM
Perhaps faster than speed of light here is analogous to the following:

* Think of a solid ball
* Drill a hole thru it
* Shine a flashlight through the hole
* Light will travel at the speed of light from one point on the ball to the other at the speed of light
* For the 2D inhabitants on the surface of the ball if any, It would seem that there was a faster than speed of light reach across their 2D plane of existence while in fact nothing did ever travel faster than the speed of light

In other words it's the extra-dimensional reach of gravity which is said to travel apparently and possibly up to 125% faster than the speed of light across the 3 dimensions of our universe.

Or, the more likely scenario where I have misunderstood the whole thing. :)

dgavin
2007-Jul-14, 07:34 PM
General relativity requires that gravity travel at the speed of light. Astronomical observations tend to confirm this expectation. The 1993 Nobel Prize in Physics (http://nobelprize.org/nobel_prizes/physics/laureates/1993/index.html) was awarded to Russell Hulse & Joseph Taylor, for their joint discovery of binary pulsar PSR 1913+16 (http://astrosun2.astro.cornell.edu/academics/courses//astro201/psr1913.htm). The pulsar period is observed to decay at a rate predicted by general relativity, where orbital energy is expected to be converted into gravitational waves, and the waves are generated because of the finite speed of propagation of gravity. The fact that observations match general relativistic expectations is consistent with the general relativistic requirement that the finite speed of gravity is in fact the speed of light. The fact that it travels so fast is the reason that it is not "simple" to see the speed of propagation of gravity. See, i.e., Hulse & Taylor, 1975 (http://adsabs.harvard.edu/abs/1975ApJ...195L..51H); Taylor, et al., 1976 (http://adsabs.harvard.edu/abs/1976ApJ...206L..53T); Taylor, Fowler & McCulloch, 1979 (http://adsabs.harvard.edu/abs/1979Natur.277..437T); Taylor & Weisberg, 1982 (http://adsabs.harvard.edu/abs/1982ApJ...253..908T).

Fomalont & Kopeikin, 2003 (http://adsabs.harvard.edu/abs/2003ApJ...598..704F) claims to have measured the speed of gravity by using a quasar close approach to Jupiter. But their claims are in dispute and have been steadily discussed since then.

Well excpet for the fact that Black Holes put a kink into a finite speed of Gravity Theroy, as then Gravity should not be able to escape a black hole, at all. That is the one paradox/counter argument to a finite gravity propagation theory. If the Speed of Gravity is finite then a black hole should litteraly collapse to a point where even it's gravity vanishes beyound it's own event horizon.

Which means we etiher don't have a clue about why it can still escape a black hole, or means that einstiens earlier work on gravity simply being warped space time is the correct model, it which case it's not information transfer and not contrained to any speed limit.

One can go nuts trying to figure out that paradox of gravity.

publius
2007-Jul-14, 09:57 PM
No, black holes don't put a kink in the finite propagation speed of gravity. General Relativity is entirely consistent with this, it just doesn't work like our minds, with Newtonian/Euclidean notions, think it ought to work.

All these things get coordinate dependent in very complex ways. But basically, gravity doesn't have to escape a black hole. As something collapses to black hole, it leaves the gravity well behind it. Stationary to that black hole, space-time is static. Indeed, in the invariant sense of things, that space-time is static to all observers.

You say, but what if you see it moving? Well, one can simply say well that's an observer moving in static space-time, not a dynamic space-time against a stationary observer. :) But, consider the moving observer anyway. One never sees that collapsing mass cross its own event horizon in finite time. You just "see" a spherical chunk of mass frozen in time. Get to moving and see you that frozen mass moving, with the changes in space-time moving with it. No information has to get out of the horizon, because you haven't seen any of the sources cross it.

Now, one can construct a truly dynamic space-time. Consider something falling into the black hole and wiggling mass around as it falls, creating changes in space-time that must propagate out.

Those changes get slower and slower and take longer to reach a distant location, but they get out. Now, if in its own frame it still wiggles after it crosses, those changes never get out. But external observers never see it anyway, because it never happens in finite time on their clocks.

We can construct a similiar thing in roughly flat space-time with a Rindler observer. To an inertial observer, there is an horizon chasing after him at light speed, getting closer and closer but never catching. Light fired after than horizon line passes will never reach him.

Now, rather than light, let's wiggle some masses around. The changes in space-time propagate outward at c, but never catch the Rindler observer. He never sees it. To us, there is no problem, we just see a "ripple" of changes in space-time whose wavefront never catches the Rindler observer. So he will never be affected by that change. To him, it never happens.

-Richard

a1call
2007-Jul-15, 05:54 PM
* Is the speed reduced through matter as is the case with light?
* Are there phenomena such as refraction, reflection, scattering involved?

I would like to elaborate further on the implications of the finite speed of gravity.

* For the sake of this argument we will assume that gravity's influence travels at the speed of light.
* Is GR compatible with the following:
** Something (say gravity) travels with the "speed of light in vacuum" through matter. Effectively traveling faster than light would through that matter
* Assuming it is incompatible(In other words speed of gravity's influence will have to drop through matter), would that indicate that gravity waves would refract when entering through an angle.
* Wouldn't refraction indicate that gravity will have to demonstrate the internal reflection phenomena?

Trouble1957
2007-Jul-30, 02:09 PM
What will happen when there is no gravitaional pull in our solar system?
:ph34r: This is not homework question :ph34r: LOL

Well, I've read this thread and still am having a hard time wondering about the OP's question and its relevance. Since gravity and mass are interdependent, to wonder what would happen if the solar system had no more gravity is equivalent of wondering what it would be like with no mass.

Seems a bit silly to wonder about lack of gravity when we aren't even around to notice one way or the other since we are part of the mass.

Oh well....................is the Sun expected to disappear some time soon? I just bought new Sunshades too....darn!

John Mendenhall
2007-Jul-30, 03:43 PM
Try the article "Speed of Gravity" in Wiki.